My 914 quit running this morning. Lost ALL power. I managed to get a meter
and traced it back. This device:
Click to view attachment
was in the harness just down from the battery. The battery wire comes from the
left, and 4 wires go to the right. It was hot to touch, so I removed it and the
wires. One was shorted to ground so I disconnected it and the car started.
No lights worked, but I was able to get home. I finally found that something was
shorting in the fuse block, and I was able to get everything working again. Oh
yeah, my flaky tach is working again!!

Does anybody know what this thing is? My guess is suppression diode or
something like that. But I don't know how current gates back from the alternator
to the battery??

It is about an inch long and about 1/2 inch wide. It says 12V30A on it. I am glad
it was there, as it limited the current draw and kept the battery from being shorted
too!

Thanks,

Jeff

That thar be a circuit breaker. Never seen one on a 914, it's probably something a previous owner added. Some of them have a heating element in them, so they stay tripped until the overload is removed. I'm guessing since it was warm, it is that type.

some DAPO "bandaid fix" for something else wrong in the electric circuit ...

if that's how the PO went about "fixing" things, i'd be afraid what else might lurk in there ...
Andy

Thanks guys! Yeah, I'm watching the car closely in case I see more problems.
At least I know about this now! It's a good "feature" though, safer!

To some it may look strange but I think it was a way for the PO to have all the positive wires in one spot away from the batery. The battery FEED cable which I assume is the one on the top could stand to be a little heavier since it is of the same gage as ONE of the others from the other circuits. Another question arose of the 30 amp deal. If you draw more current from your circuit than that, ie. huge radio amp, it might trip. To make this thing even safer. the fuse should be the first thing to connect from the battery as opposed to the battery cable itself.

Interesting non the less.

I agree with JPB's analysis. I will probably increase the size of the feed wire, if
I do not get sidetracked by newer problems!

It is a good feature, no matter what the reason for its installation. If I need
it, I might add another of these devices to feed other circuits I create.

I didn't show the battery, but there are just two wires there. One is the very
heavy wire to the starter, and this one that connects to the circuit breaker. This
first wire is about 8 inches long.

and i think it's a ticket for disaster.
that's exactly the kind of thinking that results in a big pile of charcoal, formerly known as a 914 ...

"hey, let's just put this 30amp thing in here so i can overload my electrical system without having to think about what i'm doing.
after all, the 30amp thing will melt first, right?"


i'd be rather suspicious why the PO deemed this "improvement" necessary ...

but hey, that's just me, your car, your bonfire ...
Andy

It's a thermal switch.

If something goes wrong in the ground, it kills the circut.

Jeff: Just by it being there it tells me that something is wrong with the electrical system. The system is perty straight forward. If you have to do a 30 amp circut breaker in line with the positive side to be safe, something is taking to much power.
:PERMAGRIN: Joe

Andy, I don't see how a cct breaker could 'cover up' other electrial problems. Like any other cct breaker it is there to protect you from other failures which in harnesses this old are all too common. If Jeff did not have that cct breaker what shape do you think his car would be in after that short in the fuse box? Bloody good re-engineering if you ask me - unfused ccts are an accident waiting to happen.

The only down side I can think of is that if that breaker pops your engine will die which in traffic could be scary! (think about the old 'if Microsoft built cars' ditty). Make sure that it is sized properly (including the feed wire) so it has lots of spare current when the car is under full electrical draw and it then becomes a major improvement. At least IMHO

Thanks Steve! You said what I have been thinking, and not sure how to phrase it.

I guess the other question is how to fix the underlying problem? How do you find
an intermittent short in a 30 year old car? What would you do if you had an
intermittent short? Put the car on jackstands? it?

I was an electrical engineer, now retired. I would add something like this to a
circuit to protect it while I searched for the correct solution. I would add it to
protect the wires as they run forward to the fuse block. We are talking about 8
inches of unprotected wire now, instead of 6 feet through the firewall, up the
tunnel, and across the dashboard!

The size of the circuit breaker/thermal switch is 30 A. That is a reasonable size.
The short apparently was not beyond the fuses, since they did not blow.

So, seriously, how would YOU fix it "right"? I am not ignoring the problem. It
scared me when the car shut down. I was awfully glad I was driving a car with no
power accessories! But, I was glad the breaker was there!!! It worked perfectly.
The battery is still intact, no burned wires, no fire! I was able to get home, without
lights, but I made it! I will fix the short, when I find it. The best way is by driving
the car to shake something loose!

Jeff

Did you not find something in the fuse panel that accounted for the failure?

Intermittents are always a glorious pain in the butt. They have to be in failed mode to do any decent trouble shooting. I'm afraid I can't offer much advise on how to proceed other than the classic isolate and test.

I'm not really familiar with the wiring up there and confess that it confuses the heck out of me but ...
There are two power lines which run forward - one to the power distribution block and one to the ignition switch. The bad one would have to have been the one to the power distribution block. But if that was the case you would have been without more than just headlights. It is really scary how many unfused devices there are hung off that power block:

Fresh Air blower relay
Dimmer relay
headlight switch ...

Pick your poison.

hmm. If the PO installed this after a similar incident and not just as a safety thing you might be able to find some wires that are cooked.

good. there's two ways to "fix it right" and they depend on how bad it is.
i'd need to see your car in person to tell you ...

btw. i don't understand where you get the impression from that there are many unfused circuits in a 914. that simply is not true.

also, i'd suspect any custom wiring first, look behind the dash for custom radio/speaker wiring etc.


1. find the problem. be systematic. start in the front and work your way back to the rear of the car. start with the sidemarkers, then blinkers, then headlights/motors, foglamps, horns, etc. you check each single wire and work your way through the car.
tiedious (sp?), but if your harness is in overall fair condition and mostly unmolested, this will work.
and you'll be learning something about your cars electricals in the process.

2. if the harness is in bad shape, lots of PO cutting and adding and looking under the dash reminds you of a bowl of sphagetti, your best bet is to simply replace the complete main harness with a good one from a donor car.
that's what i ended up doing on my car. cost me ~100 bucks for the harness and two weekends to swap it ...


Andy

30A blew here fellas. This is not a little 5A fuse. I think it fried because the feed probably super heated during normal running thus transfering that heat to the 30A monster. The feed probably could handel more that 30A and thus looks okay. If the demand for all the other circuits was high, this would happen. If the short was on one of them red wires, he would see some smoke and a significant power loss in a specific circuit if it didn't fry next to the fuel line. Fuses also save powered units in the circuit like electric motors, relays ect. and allows a wire problem to stay a wire problem which can be cheaply removed and replaced. If one has no fuse in a large circuit, then things can smoke from all over the vehicle and multiple items may need replacing only if the vehicle does not burn up first.

Nothing wrong with having extra fuses in the circuit, however, it may prove troublsome if to many of them fried at once.

I consider a wire directly from the battery until it gets to the fuse panel unfused!
I THINK the problem was a metal relay that was laying on the wires in the fuse
block was the problem. I am not sure. I can only guess about the PO's
intentions. There are no burned wires visible on the tunnel or in the fuse block
area, I checked. There looks to be very little molested in the car at all. I did
remove one extra hot wire from the fuse block, perhaps the old radio power, but
that is all.

Being an electrical guy, I will continue to try to find the problem. I don't like
mysteries much either. I am just not going to make it my life's work right now.

Maybe circuits is a bad choice of words. There are a number of devices other than fuses that are connected to that power distribution block. If any of them short they are not protected by a fuse and will draw current until they burn up. Follow the red wires - for the most part Porsche seems to have used Red as the standard for unfused power.

agreed - particular emphasis on anything patched in upstream of a fuse.


Good advise - systematic is always faster in the long run. Remember though that none of the individual fuses blew. This suggests the problem is upstream of the fuse box - anything that is fused is unlikely to be the culprit. I suppose though that the cct breaker could have reacted to an overload on one of the fused ccts before the OEM fuse burned. That might pop the breaker and leave the fuse intact. Seems a little unlikely but it could happen.

The real beast here is that it is intermittent not a hard failure. Really hard to find them.

Before you call it a wrap you might want investigate that loose relay - that just doesn't sound right. Perhaps another 're-engineering' by the PO to fix hot start problems by using a relay instead of the switch contacts for the solenoid? Perfectly fine in my books but the relay should be properly mounted - not left loose?

i wouldn't start at the front and work back. i would find what circut is the problem by useing a volt ohm meter and test for shorts [close to 0 ohms] off the fuse panel. and isolate by finding the splice points and check there.
if you had a metal breaker or flasher laying on the back side of the fuse panel that is highly likely the problem.
electrical trouble shooting is what i do 10hr a day 4 days a week.